1. Field of the Invention
The invention generally relates to a motion estimation and compensation technique, and more particularly, to a motion vector refining apparatus which can increase vertical resolution of an image.
2. Description of Related Art
Existing image display techniques usually adopt an interlace scan mode (usually applied to cathode ray tube (CRT) TVs) and a progressive scan mode (usually applied to digital TVs or digital cinemas). In the interlace scan mode, only half of the scan lines in an image are transmitted or played each time (i.e., scan lines in odd numbers (referred to as an odd field) and scan lines in even numbers (referred to as an even field) in the image are alternatively played). Since each field only contains data of the scan lines in odd or even numbers, vertical discontinuity is produced in a displayed image. Contrarily, in the progressive scan mode, the scan lines in an image are played one by one. However, the frame rate in the progressive scan mode is usually much lower than that in the interlace scan mode. Accordingly, image discontinuity or motion blur may be produced in a displayed image.
In order to increase image resolution and smoothness and avoid image discontinuity and motion blur, conventionally, a “motion adaptive deinterlacing” technique is adopted to increase the vertical resolution in a motion image in the interlace scan mode. In recent years, a “motion compensated deinterlacing” technique is further adopted to increase the vertical resolution of an image. In the motion compensated deinterlacing technique, the motion trajectory of a moving object in an image is predicted, and new pixel data is interpolated on the motion trajectory, so that the lost field can be effectively compensated and the resolution in the vertical direction can be effectively retained. Accordingly, image motion is made very clear and image blur is avoided. Regarding the progressive scan mode with lower frame vertical resolution, the lost part of an image can be interpolated on the time axis through the technique described above, so that the vertical resolution of the output image signal can be increased.
In the motion compensated deinterlacing technique, in order to make the motion vectors of the same moving object to be distributed more consistently, a smooth processing is performed on the motion vectors of neighboring macroblocks to reduce the variations of the motion vectors. However, motion vector estimation error, and accordingly image defects (for example, halation), may be produced when the smooth processing is performed at where the images of two moving objects meet each other or at the edges of dynamic and static areas. Thereby, an estimation and compensation technique for refining motion vectors is desired.